1. Field of the Invention
The present invention relates to a coaxial cable producing method and a coaxial cable and particularly, to a method of producing a coaxial cable of which the metal plating layer formed by impregnating a metal woven shielding conductor layer with a molten metal is improved at its inner surface in the smoothness and thus its adhesivity to an insulated cable is increased and to such a coaxial cable.
2. Description of the Prior Art
As high frequency coaxial cables enhanced in the electric characteristics including the suppression of reflection and attenuation in a high frequency range, semi-rigid type coaxial cables are known in which an insulated cable produced by coating a center conductor with an insulator layer is coaxially covered at its outer surface with a metal pipe made of, for example, copper or aluminum.
The semi-rigid type coaxial cables using the metal pipe are however high in the production cost and poor in the flexibility, hence making the wiring operation difficult.
Alternatively, modified coaxial cables which are decreased in the production cost and improved in the flexibility although their electric characteristics including the suppression of reflection and attenuation are lower than those of the semi-rigid type coaxial cables using the metal pipe have been proposed comprising an insulated cable produced by coating the outer surface of a center conductor with an insulator layer and covered with a metal woven shielding conductor layer and a metal plating layer produced by passing the insulated cable through a molten metal plating solution to impregnate the metal woven shielding conductor layer with a molten metal.
FIG. 10 is an explanatory view showing a process of forming the metal woven shielding layer in a modified coaxial cable producing method using the molten metal plating.
An insulated cable W formed by coating the outer surface of a center conductor (102 in FIG. 11) with an insulator layer (103 in FIG. 11) with the use of a common means at the previous step is released from a supply reel 20, passed on a guide roll 21, and directed into a dice 24.
Also, a group of metal conductor wires 14 are woven with reels 25, on which the metal conductor wires 14 are wound, spinning about the insulated cable W at the entrance of the dice 24 to form a metal woven shielding conductor layer (104 in FIG. 11) over the outer surface of the insulated cable W.
A resultant intermediate cable 111 having the metal woven shielding conductor layer (104 in FIG. 11) covered over the outer surface of the insulated cable W is drawn by the action of a drawing capstan 22 and taken up on a take-up reel 23.
FIG. 11 is a cross sectional view of the intermediate cable 111.
The metal woven shielding conductor layer 104 of the intermediate cable 111 is closely bonded to the outer surface of the insulated cable W.
FIG. 12 is an explanatory view showing a process of forming a metal plating layer in the method of producing a coaxial cable using the molten metal plating.
The intermediate cable 111 is released from a supply reel 51, coated with a flux by a flux coating apparatus 52, guided by a guide roller 53A, and directed into a molten metal plating solution 55 in a molten metal plating tub 54. Then, the cable is guided by a guide roller 53B in the molten metal plating tub 54, moved out from the molten metal plating solution 55, passed through a plating solution squeezing dice 56 disposed above the molten metal plating solution 55 for adjusting to a desired thickness of the plating, cooled down by a cooling apparatus 57 to complete a coaxial cable 101, guided by a guide roller 53C, and taken up on a take-up reel 58.
FIG. 13 is a cross sectional view of the coaxial cable 101 produced by the coaxial cable producing method using the molten metal plating.
The coaxial cable 101 comprises the insulated cable W formed by coating the center conductor 102 with the insulator layer 103 and the metal plating layer 105 formed on the insulated cable W by impregnating the metal woven shielding conductor layer 104 with the molten metal.
FIG. 14 is an exemplary diagram of the attenuation and reflection characteristics of a transmission signal on the coaxial cable 101.
A one-meter length of the coaxial cable 101 was prepared and its reflection and attenuation characteristics at a high frequency range from 0.045 GHz to 18 GHz were measured with a network analyzer.
Peaks of the reflection and the attenuation which may result from the effect of a winding pitch of the metal woven shielding conductor layer 104 are shown at about 10 GHz of a transmission frequency.
Also, the standing wave ratio of a reflected voltage at a high frequency range from 0.045 GHz to 18 GHz is 1.4.
In the conventional method of producing a coaxial cable using the molten metal plating, the metal woven shielding conductor layer 104 is adhered closely to the outer surface of the insulated cable W during the step of forming the intermediate cable 111 as shown in FIG. 11. When the intermediate cable 111 is immersed in the molten metal plating solution 55, for example, at 260xc2x0 C., the insulator layer 103 made of a resin material is thermally expanded hence biting into the metal woven shielding conductor layer 104. This causes the metal woven shielding conductor layer 104 to be hardly impregnated with the molten metal. Accordingly, when the insulator layer 103 is cooled down and returns to its original size, portions of the metal woven shielding conductor layer 104 are exposed from the inner surface of the metal plating layer 105 thus generating gaps and undulations of the surface.
If there are generated gaps and undulations of the inner surface of the metal plating layer in which a high frequency current runs, the high frequency characteristic may be declined. More particularly, peaks of the reflection and attenuation which may result from the effect of a winding pitch of the metal woven shielding conductor layer 104 appear about at 10 GHz of the transmission frequency, hardly ensuring the effectiveness within a frequency range including 10 GHz.
In addition, the adhesivity between the insulated cable W and the metal plating layer 105 is poor, causing the metal plating layer 105 to be easily slipped out.
It is an object of the present invention to provide a coaxial cable producing method and a coaxial cable of which the metal plating layer formed by impregnating a metal woven shielding conductor layer with a molten metal is improved at its inner surface in the smoothness and its adhesivity to the insulated cable is increased.
As a first aspect of the present invention, a method of producing a coaxial cable is provided comprising the steps of covering with a metal woven shielding conductor layer an insulated cable formed by coating the outer surface of a center conductor with an insulator layer, and passing the cable through a molten metal plating solution to impregnate the metal woven shielding conductor layer with a molten metal to have a metal plating layer, said step of covering with the metal woven shielding conductor layer being arranged in which the insulated cable is accompanied with one or more solder or tin wires while the metal woven shielding conductor layer is being woven.
In the method of producing a coaxial cable as the first aspect, when the intermediate cable having the insulated cable associated with one or more solder or tin wires is immersed in the molten metal plating solution, the solder or tin wires are dissolved into the molten metal plating solution thus generating a spatial margin between the insulated cable and the metal woven shielding conductor layer. This prevents the insulator layer from biting into the metal woven shielding conductor layer when it is thermally expanded. Accordingly, as the metal woven shielding conductor layer is impregnated deeply with the molten metal, there are generated no gaps or undulations on the inner surface of the metal plating layer. Hence, the coaxial cable will be improved in the suppression of reflection and attenuation of a transmission signal. Also, the metal plating layer will hardly be slipped out.
As a second aspect of the present invention, a method of producing a coaxial cable is provided comprising the steps of covering with a metal woven shielding conductor layer an insulated cable formed by coating the outer surface of a center conductor with an insulator layer, and passing the cable through a molten metal plating solution to impregnate the metal woven shielding conductor layer with a molten metal to have a metal plating layer, said step of covering with the metal woven shielding conductor layer being arranged in which one or more spacer wires are provided between the insulated cable and the metal woven shielding conductor layer during the weaving action and removed out when the weaving action is completed.
In the method of producing a coaxial cable as the second aspect, one or more of the spacer wires are removed from the insulated cable when the weaving action has been finished, thus generating a spatial margin between the insulated cable and the metal woven shielding conductor layer in the intermediate cable. This prevents the insulator layer from biting into the metal woven shielding conductor layer when it is thermally expanded as the intermediate cable is immersed in the molten metal plating solution. Accordingly, since the metal woven shielding conductor layer is impregnated deeply with the molten metal, there are generated no gaps or undulations on the inner surface of the metal plating layer. Hence, the coaxial cable will be improved in the suppression of reflection and attenuation of a transmission signal. Also, the metal plating layer will hardly be slipped out.
As a third aspect of the present invention, a method of producing a coaxial cable is provided comprising the steps of covering with a metal woven shielding conductor layer an insulated cable formed by coating the outer surface of a center conductor with an insulator layer, and passing the cable through a molten metal plating solution to impregnate the metal woven shielding conductor layer with a molten metal to have a metal plating layer, said step of covering with the metal woven shielding conductor layer being arranged in which the metal woven shielding conductor layer is woven while the insulated cable is being heated to thermally expand the insulator layer.
In the method of producing a coaxial cable as the third aspect, the metal woven shielding conductor layer is woven while the insulator layer is being thermally expanded. The resultant intermediate cable is thus obtained with the metal woven shielding conductor layer fitted closely to the insulator layer thermally expanded. This prevents the insulator layer from biting into the metal woven shielding conductor layer when it is thermally expanded as the intermediate cable is immersed in the molten metal plating solution. Accordingly, since the metal woven shielding conductor layer is impregnated deeply with the molten metal, there are generated no gaps or undulations on the inner surface of the metal plating layer. Hence, the coaxial cable will be improved in the suppression of reflection and attenuation of a transmission signal. Also, the metal plating layer will hardly be slipped out.
As a fourth aspect of the present invention, a method of producing a coaxial cable is provided in that the coaxial cable produced according to the method of producing a coaxial cable as any of the first to third aspects is reduced in the diameter with the use of a dice or a swaging machine to eliminate the space and thus increase the adhesivity between the insulator layer and the metal plating layer.
In the method of producing a coaxial cable as the fourth aspect, the coaxial cable is reduced in the diameter using a dice or a swaging machine, thus eliminating the space and improving the adhesivity between the insulator layer and the metal plating layer. Accordingly, the coaxial cable will be improved in the suppression of reflection and attenuation of a transmission signal. Also, the metal plating layer will hardly be slipped out.
As a fifth aspect of the present invention, a coaxial cable is provided having an insulated cable produced by coating the outer surface of a center conductor with an insulator layer and covered with a metal plating layer formed by impregnating a metal woven shielding conductor layer with a molten metal and particularly characterized in that the metal plating layer is arranged smooth at its inner surface and adhered closely to the outer surface of the insulated cable.
The coaxial cable as the fifth aspect allows the metal plating layer to be smooth at its inner surface and adhered closely to the outer surface of the insulated cable. Accordingly, the coaxial cable will be improved in the suppression of reflection and attenuation of a transmission signal. Also, the metal plating layer will hardly be slipped out.